This invention relates generally to hand-held and manually operated flashlight assemblies, and is more particularly directed to flashlights and the like of the type having batteries which may be repeatedly recharged for extended use.
Presently, the most common flashlights are of the type using replaceable primary batteries, such as zinc-carbon, which are limited to a single discharge and typically have limited shelf life. Some flashlights are provided with batteries of the type especially adapted to being recharged, such as nickel-cadmium batteries. Some such units incorporate therein recharging units for the batteries, so that the unit may be plugged into a conventional wall outlet or other power source for recharging of the batteries. In other flashlights, auxiliary recharging devices are provided as separate units to enable recharging of the batteries in the flashlight from various sources of power. While such arrangements have definite usefulness, it is apparent that their operating time in field use is still limited to a single charge on the batteries and by self discharge characteristics, and hence they cannot be used for extended periods of time if separated from normal sources of power. In addition, unless constant care is taken on the part of an operator to maintain the charge on the batteries, the units may not be available for use in times of emergency.
Other flashlight units in the past have incorporated various forms of manually operated generators to enable the operator to use the device without prior charging, such devices having the advantage that they are continuously available for use whether in emergency situations or in the event extended operation remote from conventional power sources is necessary. Such flashlight assemblies have the disadvantage, however, that the constant operation becomes fatiguing and that there is no light available if operation is stopped more than momentarily, thus the use of hands for other manipulations is not possible. In addition, typical generator characteristics are not generally completely amenable to this form of operation, for example, due to variations in instantaneous output voltage which include high and low extremes that are detrimental to the lamp load's life and/or performance, and as a result many such units have been employed with additional structures such as fly wheels to attempt to stabilize the output voltages. Such expedients of course increase the complexity as well as the overall weight of the devices. In addition, the lamps are run in an undervoltage mode, with sacrifice to brightness and efficiency.
While stationary or vehicle carried lighting devices utilizing engines as the prime movers have been employed incorporating generators and rechargeable batteries connected to be charged by such generators, arrangements of this type are typically large and cumbersome, and even though such systems present many highly evolved specific functional advantages, such large engine driven systems are not adaptable to units such as flashlights that could be carried and handled by the average person. In addition, such devices are noisy and require fuel.
It is therefore an object of this invention to provide a unitary hand-held flashlight assembly device which includes a manually operable generator and rechargeable batteries and includes a load device such as an electric lamp, and which overcomes the above disadvantages of the previously employed devices.
Briefly stated, in accordance with the invention, a unitary hand-held flashlight device incorporates a manually operable generator, one or more rechargeable batteries, such as low impedance pressure vented batteries, such as nickel, and, as a typical useful end load, a flashlight lamp assembly.
The generator is connected to charge the battery, for example by way of a torque switch or speed switch or the like, so that the battery is not discharged by the generator windings at low speeds or standstill, the output voltage of the generator being greater at convenient cranking speeds than the battery terminal voltage. The battery serves as a storage device for the output of the generator, as well as acting as a voltage regulator, to permit use of the load, e.g., a flashlight, for extended time periods without operation of the generator. The load may be connected to the battery by any suitable switching device. The recommended nickel-cadmium battery offers additional advantages over other battery type lights, such as indefinite shelf life when stored in the discharge state.
The operating characteristics of rechargeable batteries, such as nickel-cadmium batteries, do not permit unlimited design possibilities with respect to the charging circuit. While such batteries may be rapidly charged with relatively high currents, such charging can only be done safely for a limited length of time and only to a portion of full capacity, this being dependent upon the cell construction, on the charge initially stored in the battery and on cell temperature, which is in turn dependent upon duty cycle and ambient temperature. If a fully charged battery is subsubjected to high charging rates, it may cause damage to the battery, as well as possible explosion in unvented cells, as a result of thermal and gassing effects. While it has been proposed that the charging rates, at least insofar as rapid charging rates are concerned, be controlled as a function of the cell temperature and/or voltage, such control techniques are difficult unless thermal sensing means are provided within the battery, since external sensing devices for controlling the charging do not accurately reflect the actual temperature within the battery in sufficient time to inhibit excessive charging. One technique for overcoming this problem is to dump the charge on the battery, so that the battery may be charged at a high rate for a predetermined period of time with safety. Such techniques, while satisfactory for some purposes, are not readily acceptable in flashlight units especially when intended for manual operation where the limit of input work endurance is critical. In this application it is preferable, practical and possible to use the dimming of the flashlight as an indicator of the state of discharge, suitable for accepting a fast charge without cell overcharge. In another technique for charging the batteries, a much lower charging rate is provided, for example 1/10th of the ampere hour capacity of the battery. While such a charging rate may in general safely be used on such batteries even though they are fully charged, the disadvantage arises that it takes an excessively long period of time, e.g., up to about 14 hours, to completely charge a discharged battery. While such low charging rates may be acceptable in some circumstances, such as when employing the rechargeable batteries in a seldom-used flashlight that can be charged by conventional power sources, such low charging rates would not normally be considered to be of value in a manually regenerated unit, since it would appear to be a great disadvantage to require such excessive periods of time in the manual recharging of the unit. Such considerations, which are apparent from cursory investigation of the characteristics of the batteries, in the past have led others to the conclusion, from the standpoint of prior concepts, that employing rechargeable batteries in a combined generator and flashlight assembly would not be either useful or practical, and consequently at this time assemblies of this type are not commercially available.
In order to overcome this problem, the present invention provides a generator capable of supplying output current at a rate to permit fast charging of the nickel-cadmium batteries, in order to overcome the undesirability of excessively long charging times. The duration and effort of the charging, however, is related to the energy that the average individual will be willing and able to expend in charging the batteries. In addition, it is desired to charge only to a fraction of the rated battery capacity to provide a safety margin. Thus, in the selection of a generator and the design of gearing between the generator and the manually operated turning device, the torque of the generator, the speed of rotation of the generator, the length of the crank arm, and the gear ratios are selected so that the average person will not under normal circumstances exceed a fraction of the capacity of the system and thereby damage the batteries, but is able to attain a useful ratio of energy input time to load operating time without reaching a fatigue limit.
For example, it has been found that, with a simple hand cranking mechanism, the average individual will not readily turn a small crank at a rate much greater than about 250 rpm, and the duration of the effort will normally not exceed one minute. Considering the relationship in a conventional d.c. generator, it is known that the voltage delivered by a generator is directly proportional to its speed, while the torque of a generator is proportional directly to the delivered current. The rotational speed of the drive for the generator can be varied, by varying the parameters, for example, of a gear train between the generator and the drive, to select the desired speed for the average individual in turning the charging handle, and the charging current is thus selected also on the basis of the capability of the average individual to charge the device, so that the torque at the driving handle which may be varied by changing the crank arm length is sufficiently great to cause fatigue without attaining an excessive charge on the battery, but yet the charge rate is sufficiently great that the energy produces useful current and is not substantially lost in frictional or other losses in the device. The batteries may then be selected on the basis of the current output of the generator when being charged by the average individual. It has been found, for example, that a successful charging current in this environment is about 5-20 times the rated capacity in ampere hours of the battery. Since the voltage and power output of a generator is a function of its speed, the size and number of cells employed in series in this charging circuit are selected on the basis of the charging current, as a function of torque, and the speed of the generator.
In a further embodiment of the invention, the power pack may also be employed as a source of mechanical energy. In this arrangement, suitable remote or local switches may be provided to bypass the torque or speed switch in the unit, thereby permitting current from the batteries to flow into the generator. If a DC generator of the type having a permanent magnet is employed, it has been found that the generator may thus also serve as a motor for performing useful operations, especially since the gear train provides a large mechanical advantage. This type of motor is preferred since adjustment of brushes is not necessary in order to provide efficiently both generator and motor function. The crank of the power pack may thus be removable, to permit the shaft to be usefully employed, for example in various tools such as screwdrivers and mixers, as well as for other devices requiring mechanical actuation, for example, emergency indicators.
Since the assembly in accordance with the invention is dependent upon manual power for its operation, it is essential that all steps be taken to increase the efficiency of the apparatus. Thus when the load is a flashlight, the reflector for directing the light as a spot is preferably a parabolic reflector, and it is preferable that the reflector have a diameter as great as possible, preferably more than about 4 inches. Further, for the most efficient use of a light, the reflector or lens should have a ripple or diffuse finish, thereby spreading the light output evenly over the spot, rather than providing a spot having bright portions and dark portions as in most conventional flashlights. It has been found that, with this type of spot, the light energy is more effectively employed from the standpoint of the user. In other words, less light output is required when a diffuse reflector or lens is employed, to obtain a given visual effect, than when the reflector and lens has a smooth finish.